Erasing Scary Memories Is a Matter of Timing

We often think of memories like Polaroid snapshots, images frozen in time. But they're more like the fluid, melting pocket watches of Salvador Dali's painting The Persistence of Memory. Now scientists have developed a method that takes advantage of memory's malleability to block specific fear memories, which could someday lead to new therapies for anxiety disorders and phobias.

Each time you recall the ice cream cake and clown from your fifth birthday party, the memory is subject to change. Information about the color of the clown's polka-dotted suit, for example, becomes "unfrozen" and could change from red to blue. This process is called reconsolidation, and scientists have blocked scary memories in rats--such as the association between a specific tone and a painful shock--during reconsolidation with drugs. Unfortunately, these drugs stop protein synthesis in the brain, which would lead to terrible side effects in people.

A different approach to diminishing fear is called extinction training. In experiments with rats, scientists keep playing the ominous tone without a shock, and over time, the animals stop getting scared by the tone. Therapists use a similar method called exposure therapy to help people overcome debilitating fears, such as claustrophobia. But these methods aren't as long-lasting as the dangerous drugs.

Earlier this year, scientists reported a happy compromise that worked in rats. They timed extinction training to when the rats' brains were reconsolidating the fearful tone memory, erasing that memory in the process.

While those researchers were working with rodents, some collaborators--cognitive neuroscientists Daniela Schiller and Elizabeth Phelps of New York University and colleagues--tested the method in people. The scientists started by creating a scary memory of a blue square. They flashed blue or yellow squares on a computer screen and gave subjects a slight shock on the wrist when only the blue square appeared. After this training session, just flashing the blue square without a shock put people on edge, which the researchers measured by recording tiny currents that pass through their skin. One day later, the scientists performed extinction training by flashing the blue square repeatedly without any shocks. To trigger reconsolidation, one-third of the subjects got a reminder--a quick flash of the blue square--10 minutes before extinction training. (Reconsolidation normally starts about 3 minutes after a memory gets recalled.) Another third received a reminder 6 hours beforehand--which meant that the extinction training began well past the time when reconsolidation ended--and the final third weren't reminded at all.

When the scientists tested the subjects' response to the blue square a day later, those who received the 10-minute reminder showed no fear, while the other two groups were still freaked out by the shape. Even 1 year later, those subjects who underwent extinction training during reconsolidation still showed no response to the blue squares, while their counterparts retained the fear memory, the scientists report online today in Nature. "Because extinction training happened during [reconsolidation], we think that ... the nature of the memory changed," Phelps says.

The long-lasting effect of this method in people "blows me away," says neuroscientist Karim Nader of McGill University in Canada. Cognitive psychologist Almut Hupbach of Lehigh University in Bethlehem, Pennsylvania, is also excited about the findings, but she cautions that fear memories associated with anxiety and post-traumatic stress disorders are far more complex and stronger than the memories in this study, which may be a challenge when applying these findings to new therapies.

Phelps agrees and adds that these techniques only erased the body's response to a memory; they didn't wipe out the memory itself, like the mind-eraser in the movie, Eternal Sunshine of the Spotless Mind. "We're getting rid of the visceral response to Kate Winslet, not your recollection of [her]."